face masks have been a matter of intense debate during the COVID-19 pandemic. Early on, several government officials and health authorities
were discouraging healthy people from wearing masks—noting that there
was little evidence for the practice’s ability to prevent spread among
the general public and citing concerns that protective face coverings,
which were desperately needed by healthcare workers, were in short
supply. Gradually, however, governments began to either require or
recommend that their citizens wear face masks in public. In June, the
World Health Organization (WHO) recommended widespread mask-use as a way
to prevent coronavirus transmission. One model estimates that if at
least 95 percent of people wear masks in public between June and
October, approximately 33,000 deaths could be avoided in the US. To get
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There are three broad categories of face coverings: tight-fitting masks known as N95 respirators that are designed to filter out both
aerosols (often defined as particles that are smaller than 5 micrometers
in diameter) and larger airborne droplets, loose-fitting surgical masks
that are fluid resistant and capable of filtering out the bigger
particles, and cloth masks, which vary widely based on how they’re made.
A growing body of research supports the use of all three types of masks, though the quality of evidence varies. One of the most
comprehensive examinations to date, published in The Lancet in early
June, systemically assessed 172 observational studies—mostly conducted
in healthcare settings—looking at the effect of physical distancing,
face masks, and eye protection on the transmission of SARS-CoV-2 and two
related coronaviruses. The results revealed that N95 respirators
provided 96 percent protection from infection and surgical masks (or
comparable reusable masks made with 12 to 16 layers of cotton or gauze)
were 67 percent protective.
While research on cloth masks is much more limited, one group of researchers demonstrated that, in the lab, multilayer masks made of
hybrid materials (cotton and silk, for example) could filter up to 90
percent of particles between 300 nanometers and 6 micrometers in size.
However, it’s important to note this is only the case when there are no
gaps around the edges of the mask, which are often present when people
wear cloth or surgical masks. Indeed, the researchers’ findings suggest
that gaps around any mask can reduce filtration by 60 percent or more.
Still, scientists using computational models have reported that, in
general, widespread use of facemasks, when combined with lockdowns, may
help prevent future waves of infection.
“We’re recommending that N95s still be primarily saved for the healthcare situation,” says Kirsten Koehler, a professor of
environmental health and engineering at Johns Hopkins University. “For
individuals in the public, wearing a fabric mask is probably still the
way to go.”There are several factors, including the number of layers and
type of material they are made from, that contribute to how effective a
mask will be, explains Raina MacIntrye, a professor of global
biosecurity at the University of New South Wales in Australia. According
to the WHO, fabric masks should ideally have at least three layers: an
inner layer made with absorbent material (e.g., cotton), an outer layer
with water-resistant material (e.g., polyester), and a middle layer
(made with absorbent or water-resistant material) to act as a filter. In
addition, MacIntrye adds, “the design should fit around the edges of
the face because air will flow down the path of least resistance.” In
other words, if there are gaps on the sides of your mask, your breath
will slip through those cracks instead of being filtered through the
Although evidence is building to support the use of masks to stem the coronavirus’ spread, many questions remain, such as whether the
coronavirus spreads through aerosols or just through larger respiratory
droplets. There is also little research on the efficacy of face masks,
particularly cloth ones, in stopping the spread of COVID-19 in community
settings, Julii Brainard, a senior research associate at Norwich
Medical School in the UK, tells The Scientist in an email.
Amidst the uncertainty, what is clear is that mask wearing is not the only action people should take to slow the spread of COVID-19, Koehler
says. “None of these masks are going to be perfect, especially against
the aerosols. You want to continue to encourage people to work from
home, avoid being crowds—things like that are going to work, regardless
of how good your mask is.